The invention relates to packers and particularly to packers of the type used to seal a well screen relative to a well casing after the well screen has been set in place. The purpose of the packer is to prevent sand in the formation from passing through the connection joint between the well screen and casing. Presently, two general types of packers are in use. Lead packers use an annular block of lead with a smaller O.D. than the casing. The lead block is adapted to deform and wedge radially outwardly into the space between the top of the well screen and the casing when it is repeatedly hammered down with a tapersided swedge block. Although lead seals are relatively effective, there is considerable concern over the possibility that they can introduce contamination into a water supply.
Another commonly used packer arrangement is the so-called self-sealing packer which is made of rubber or other elastomeric material. Typically, such a packer might have the general shape of a funnel with the smaller diameter portion encircling the upper end of the well screen and clamped to it and the conical upper portion resiliently bearing against the inner wall of the casing. Such packers naturally bear against the casing wall all the time they and the well screen are being lowered into position. Where the casing wall is rough and/or the well is deep, there is a considerable risk that the rubber packer will be abraded, thus reducing the sealing pressure or preventing a seal, thereby rendering the packer ineffective.